Device for the extraction of screw-threaded wires particularly for orthopaedic surgical operations

ABSTRACT

A device for the extraction of screwthreaded sires for osteosynthesis, characterized in that it comprises: at least two lever pieces (20, 21) hinged together and having at one longitudinal end (20a, 21a) seats (22, 23) for grasping the end of a wire (19) which it is required to extract, and clamp means acting on the ohter end of said lever pieces (20, 21) to promote their opening in such a way as to generate a couple of gripping forces on the end of the wire (19). Said clamp means are of screw type and preferably consist of a threaded pin (24) fitted with a knob (24a) and screwed into a tapped piece (25) integral with the end (21b) of one of said lever pieces (21). The end (24b) of the threaded pin nearest the pivot is of a generally frustoconical shape to interact with an inclined plane surface (26) formed in the end (20b) of the other lever piece (20) in such a way as to force it outwards when said pin (24) is screwed in. The thread on said pin (24) and on the tapped piece (25) is opposite to that of the thread of the wires (19).

The present invention relates to a device for the extraction ofscrewthreaded wires for osteosynthesis at the end of treatment.

As is known from German Patent Application No. P4309707 published in thefile of DE-44,06,374-C, screwthreaded wires are an improvement on theKirschner's wires used in orthopaedic surgery for compacting bonefragments onto the main bone or in the reconstruction of small fracturedbones. Unlike Kirschener's wires, screwthreaded wires are not completelysmooth: instead, the end that is to be inserted into the bone isthreaded, and the diameter of the thread is less than that of theremaining cylindrical shank of the wire. There is thus a shoulder at thepoint where the screwthreaded part ends and the smooth part begins. Thisshoulder serves to exert a compressive action on the bone fragmenttowards the part of the bone from which said fragment has becomedetached, when the screwthreaded wire is screwed in.

Depending on the characteristics and dimensions of the bone fragment andof the bone from which said fragment has become detached, screwthreadedwires of different diameters and with different thread diameters areused, as for example 1.5-mm, 2.0-mm, or 3.0-mm diameter wires withthread diameters of 1.2 mm, 1.6 mm or 2.2 mm respectively, and withdifferent lengths of the threaded part.

When the treatment is finished, that is to say when the bone fragmenthas become firmly fixed to the bone from which it was detached, thescrewthreaded wire or wires must be removed.

A known method for the extraction of screwthreaded wires forosteosynthesis involves using ordinary forceps consisting of two leversgiving mechanical advantage which are held by their longer arms andenable a gripping couple to be produced in the two jaws provided on theshorter arms.

During the operation of extracting a wire with forceps the followingproblem can arise.

Since the operator (the orthopaedic surgeon) is wearing elastic gloveshis grip may relax as a result of slight slippages between his hand andthe tool. This produces a relaxing of the effort applied to the leversand consequently a reduction in the gripping forces, as a result ofwhich the jaws may slip on the end of the wire is to be extracted.

Also known is a wire-extracting device consisting of a spanner in whichthe opposite end from that on which the grip is formed contains acylindrical seat in which the cylindrical end of the wire to beextracted is accommodated. In the side wall of said cylindrical cavityis a set screw whose axis is perpendicular to the axis of saidcylindrical cavity. This screw can be driven from the outside by ahexagon socket wrench in order to clamp the end of the wire to beextracted.

The problem with the known extractor device is that it cannot be usedfor removing a wire whose end is completely below the skin of thepatient from whom the wire is to be extracted, The cause in order toclamp the cylindrical end of the wire to be extracted in thisinstrument, it is necessary to turn said set screw, and since the lattermust grip the lateral surface of said end, it would be necessary to workunderneath the external surface of the skin, a position which isvirtually inaccessible.

During the operations of removing the wire, the known extractor devicesmust be turned together with the wire itself, and in cases in which theend of the wire is deep below the external surface of the skin therecould be accidental impact of the instrument on the soft tissuessurrounding the end of the wire in question.

U.S. Pat. No. 4,438,769 discloses a device for holding, driving andwithdrawing a medical staple, comprising a staple retaining memberhaving spaced and opposed portions normally and inherently urged awayfrom each other and being adapted to receive and retain a medical stapletherebetween, the spaced and opposed portions having force applicationsurfaces to which force may be applied to overcome the normal andinherent urging away force to releasably retain a medical stapletherebetween; and a force applying and force reduction membercooperatively associated with said integrally constructed stapleretaining member for selective application or removal of discrete forcesupon said force application surfaces.

FR-A-1,322,212 discloses an apparatus intended to withdraw pins used inbone surgery, in particular pins in the form of threaded rods,comprising a rod, one end of which is screwed into a tube, the other endof the rod having a hole bored along its axis, the rod and the tube eachbeing provided with handles, the diameter of the hole being variable inaccordance with the tightening force which a conical end of the tubeexerts on a conical wall of the hole when the rod is screwed into thetube using the handles.

The closest prior art to the present invention is represented bydocument AUB-75,239/87 which discloses in FIGS. 3-10c and thedescription page 4, second paragraph: a device suitable for theextraction of screwthreaded wires suitable for osteosynthesis whichcomprises: at least two lever pieces hinged together and having at oneend longitudinal end seats or jaws suitable for grasping the end of awire which it is required to extract, and clamp means acting on theother ends of said lever pieces to promote their opening or closing insuch a way as to generate at least one gripping couple on the end of thewire.

The precharacterizing portion of claim 1 is based upon this prior art.

It is the chief object of the present invention to provide orthopaedicsurgeons with a device for the extraction of screwthreaded wires forosteosynthesis which can be held firmly and which, if the operator'sgrip should relax, does not relax its grip on the end of the wire.

The present invention also aims to provide a device for the extractionof a wire that would also be able to extract wires whose ends are wellbelow the external surface of the skin, requiring only a small incisioninto the skin to get at the end of the wire and also avoiding, orreducing to a minimum, the impact between the device and the soft partsof the surrounding tissues.

In accordance with the present invention there is provided a device forextracting screwthreaded wires for osteosynthesis, comprising at leasttwo lever pieces hinged together and having at one longitudinal endthereof seats or jaws for grasping the end of a wire which is requiredto be extracted, and manually operable clamp means acting on the otherend of said lever pieces to promote opening or closing thereof tothereby generate at least one gripping couple on the end of the wire,and characterized in that said clamp means are provided with means forpreventing relaxation of the grip on the end of the wire to beextracted, and said seats or jaws are provided with means for grippingthe end of the wire, said relaxation-preventing means including at leasta threaded pin mounted at one end of one of the lever pieces forselectively locking the end of the other lever piece, said grippingmeans having semicylindrical cavities whose diameter is approximatelyequal to the diameter of the wire to be extracted and whose longitudinalaxis is coaxial with the longitudinal axis of the device, and having afirst cylindrical end part whose diameter is slightly greater than thediameter of the wire to be extracted and a second, generallyfrustoconical part joining said first part and a generally cylindricalcentral part of the two lever pieces thereby to enable the wire to begripped beneath the surface of the skin.

The threaded pin is preferably fitted with a knob and screwed onto atapped piece integral with the end of one of said lever pieces. The endof the screwthreaded pin nearest the pivot is preferably of a generallyfrustoconical shape to interact with an inclined plane surface formed atthe end of the other lever piece in such a way as to force it outwardswhen said pin is screwed in. The hand of the thread on said pin and onthe tapped piece is opposite to that of the thread on the wires.

A first advantage offered by the proposed invention consists in the factthat the device has a mechanism for locking the end of the wire which itis required to extract, so that the operator can briefly relax his gripon said device without having the extraction device relax its own gripon the end of the wire as a result. Furthermore, the jaws of this deviceincrease their clamping force as the device turns with and unscrews thescrewthreaded wire by virtue of the fact that the hand of the thread ofthe clamping mechanism is opposite to that of the wire to be extracted.

A second advantage lies in the fact that the proposed device makes itpossible also to remove screwthreaded wires whose ends are buried in thesoft tissues and thus not projecting above the skin. This is due to thefact that the seats or jaws are provided with means for gripping the endof the wire below the extended surface of the skin.

Other advantages will become clear in the following detailed descriptionwhich explains a number of possible examples of embodiments of thepresent invention--no limitation being implied, with reference to theaccompanying drawings, in which:

FIG. 1 is a front view of a device for the extraction of screwthreadedwires according to the present invention;

FIG. 2 is an exploded view of the device of the previous figure;

FIG. 3 is a view from below of a first lever piece of the device shownin FIG. 1;

FIG. 4 is a view from above of a second lever piece of the device shownin FIG. 1;

FIG. 5 is a perspective view of the device shown in FIG. 1;

FIG. 6 is a perspective view of a second embodiment of the deviceaccording to the present invention;

FIG. 7 is a perspective view of a third embodiment of the deviceaccording to the present invention; and

FIG. 8 is a sectional view of a detail of the device shown in FIG. 7;

FIG. 9 is a perspective view of a fourth embodiment of the deviceaccording to the present invention;

FIG. 10 is an exploded partial perspective view of the device show inFIG. 9;

FIG. 11 is a perspective view of a fifth embodiment of a deviceaccording to the present invention;

FIG. 12 is an exploded partial perspective view of the device shown inFIG. 11;

FIG. 13 is a partial sectional view of the device shown in FIG. 11; and

FIG. 14 is a perspective view of a sixth embodiment of the deviceaccording to the present invention.

With reference to FIGS. 1 to 5, it will be seen that in a firstembodiment the device according to the invention comprises: two leverpieces 20 and 21 hinged together and having at respective longitudinalends 20a and 21a seats 22 and 23 for grasping the end of a wire 19 whichit is required to extract, and clamp means 24-25 acting on the other end20b and 21b of said lever pieces 20 and 21 to promote their opening orclosing in such a way as to generate at least one gripping couple on theend of the wire 19.

As illustrated in FIG. 1, the clamp means 24-25 are of a screw type andconsist of a screwthreaded pin 24 screwed into a tapped piece 25integral with the end 21b of the lever piece 21. The axis of forwardmovement of said clamp means 24-25 is generally parallel with the secondlever piece 21. The end 24b of the screwthreaded pin 24 nearest thepivot of said two lever pieces 20 and 21 is of a generally frustoconicalshape to interact with an inclined plane surface 26 formed at the end20b of the first lever piece 20, in such a way as to force it outwardswhen said pin is screwed in.

The hand of the threads on the pin 24 and on the tapped piece 25 isopposite to that of the thread on the wires. In this way, as theoperator continues to screw the pin 24 into the tapped piece 25, oncethe ends 20a and 21a of said lever pieces have closed on the end of thewire to be extracted, the rotation of the device is such as to unscrewthe wire and thus extract it.

The pin 24, illustrated in detail in FIG. 2, is provided, at the endopposite to that 24b of generally frustoconical shape, with a knobhaving a generally polygonal cavity 40 whose longitudinal axis iscoaxial with the axis of said pin, which cavity is suitable for theinsertion of a polygonal socket wrench (key), not illustrated in thedrawings, which facilitates the operations of screwing the pin 24 andthus unscrewing the screwthreaded wire which it is required to extract.

As can be seen in FIGS. 1 and 3, the tapped piece 25 consists of acollar with a grooved outer surface 27 suitable for use as a knob toprovide a better purchase during the extraction, by unscrewing, of thewire.

As illustrated in FIGS. 3 and 4, the opposing surfaces of the ends ofthe two lever pieces are formed into seats 22 and 23 for grasping theend of a wire which it is required to extract. Said seats consist ofsemicylindrical cavities whose diameter is approximately equal to thediameter of the wire to be extracted and whose longitudinal axis iscoaxial with the longitudinal axis of said device.

The longitudinal ends of the two lever pieces furthest from that towhich the screw-tape clams means are fitted, and containing said seats22 and 23, are each formed by a first, cylindrical end part whosediameter is slightly greater than the diameter of the wire to beextracted and by a second, generally frustoconical part joining saidfirst part and the generally cylindrical central part of the pair oflever pieces. Said end of the extractor device has been designed thusdesigned or conceived in order that, when the device is used to extracta wire whose end is buried in soft tissues, turning the device causesthe least possible damage to those tissues.

Illustrated in FIG. 6 is a second embodiment of the device for theextraction of screwthreaded wires, according to the present invention,in which, in contrast to the previous embodiment, the axis of forwardmovement of the screw-type clamp means is generally perpendicular to thelongitudinal axis of said device. In this embodiment the pin 124comprises two threaded portions 128 and 129 engaged in correspondingthreads in tapped pieces 125 formed in the ends 120b, 121b of said leverpieces 120 and 121. The threads of the threaded portions 128 and 129(and accordingly the threads of the topped pieces 125) are of mutuallyopposite hand so that turning said pin in one sense causes said leverpieces to open and turning the pin in the opposite sense causes saidlever pieces to close.

Rather than be formed directly in the ends 120b, 121b of said leverpieces 120 and 121, the tapped pieces 125 can be formed by inserting twocylindrical pieces 150, in which two tapped cavities of the samedimensions as the thread of said portions 128 and 129 are made, incorresponding cavities formed in said ends 120b, 121b of the leverpieces. This embodiment illustrated in FIG. 6 makes it possible to givethe two lever pieces 120 and 121 the right surface finishes appropriateto the type of use of the insturment separately from the threadedpeices.

FIG. 7 illustrates a third embodiment of the device for the extractionof screwthreaded wires according to the present invention, in which theaxis of forward movement of the screw-type clamp means is againgenerally perpendicular to the longitudinal axis of said device.However, as can be seen more clearly in FIG. 8, said screw-type clampmeans consist of a pair of pins 224 and 230, the first of which screwsinto the end 221b of the second lever piece of the extractor device,while the second is integral with the end 220b of the first lever pieceand, in combination with the pin 224, provides a means of holding thedevice.

FIG. 9 illustrates a fourth embodiment of the device for the extractionof screwthreaded wires according to the present invention, in which theaxis of forward movement of the screw-type clamp means is generallyparallel with one of the two lever pieces 320 and 321.

The lever pieces 320 and 321 are so formed that together they offer agenerally frustoconical shape converging towards their first ends 320a,321a, and are elastically hinged at their second ends 320b, 321b to forma body 331 to which is attached a rod 331' for screwing/unscrewing thewire to be extracted, when the jaws of the device have been clampedtightly on the end of the wire to be extracted. The gripping couple onthe end of the illustrated in detail in FIG. 10, that is generallyfrustoconical and hollow, about a threaded portion 334 of said two leverpieces which is located near the pivot of these pieces.

The ring nut 332 also includes a knob 333, knurled for easy purchase,for bending the two lever pieces so that their ends 320a, 321acontaining the seats 322 and 323 for gripping the end of a wire to beextracted, squeeze the end of this wire.

FIGS. 11 and 12 illustrate a fifth embodiment of the present inventionthat differs from that described immediately above in that the two leverpieces 420 and 421 are formed in such a way that together they present agenerally frustoconical shape converging towards their second ends 420b,421b near the pivot.

FIG. 13 is a longitudinal section through the device depicted in FIGS.11 and 12 with the locking ringnut 432 fully screwed onto the threadedportion 434 of the body 431. In this position the device is ready toaccommodate the end of the wire to be extracted in its seats 422 and 423formed at the ends 420a and 421a of the two lever pieces 420 and 421.The couple of forces required to grip said wire end is produced simplyby partly unscrewing the ringnut 432 so that it moves towards the ends420a and 421a of said two lever pieces.

It is clear in FIG. 13 that the two lever pieces 420 and 421 can be madeas a single part which is then fixed to said body 431 by means of a pin435 or any other suitable means for fixing the two parts together.

The two lever pieces and the body can obviously equally well be made asa single part, as in the embodiment illustrated in FIG. 10. Likewise theembodiment illustrated in FIG. 10 can obviously be made with the twolever pieces 320 and 321 in a single part which is then fixed to thebody 331 by means of a pin or any other suitable means for fixing thetwo parts together.

This embodiment has the advantage that the locking ringnut 432 is unableto unscrew itself on its own from the pair of lever pieces 420 and 421.

This is because in order to remove the locking ringnut 432 completelyfrom the pair of lever pieces 420 and 421 it is necessary to apply aforce parallel to the longitudinal axis of the extractor device. Whenthe ringnut 432 has been unscrewed from the threaded portion 434 and isslid in the longitudinal direction, its internal surface comes intocontact with the external surface of the two lever pieces 420 and 421which, because they taper down towards their pivot, prevent the ringnutfrom working itself loose. Only if the two lever pieces are bentelastically and their ends 420a and 421a brought together can theringnut slide longitudinally far enough to come completely off thedevice. This prevents the ringnut from accidentally working itself looseduring the earlier operations of gripping the end of the wire which itis required to extract.

Lastly, FIG. 14 illustrates a sixth embodiment of the invention, inwhich the two lever pieces 520 and 521 are hinged together by a pin 539to form forceps. A return spring 544 is inserted close to said pin toenable the extractor device to remain in the open position in theabsence of external action, that is to say with the ends 520a and 521a,containing the seats 522 and 523 for gripping the end of a wire to beextracted, apart.

The clamp means consist of a lever device 541 comprising a camming rod542 and a ring 543 for the pivoting of said rod 542. Said ring is alsoanchored, at the opposite side from that secured to said rod 542, to oneend 521b of one lever piece 521 of the extractor device.

The ring 543 could obviously equally well be anchored to the lever piece520, in which case the rod 542 would act on the end 521b of the leverpiece 521.

The lever device 541 is so located as to enable the operator who isholding the extractor device to act on the end 542a of said lever toforce this end 542a towards the piece 520, thus increasing the grippingcouple on the end of the wire which it is required to extract, for by sodoing the device 541 is made to exert a force on the lever piece 520 atthe point of contact of the suitably shaped rod 542 with the end 520b ofthe lever piece 520, so tending to close or urging together the two ends520b and 521b of the two lever pieces. The closer the end 542a of therod 542 comes to the piece 520, the more the two lever pieces 520 and521 of the extractor device are forced to squeeze the jaws 520a and 521aof said device, and thus produce the couple of forces necessary to gripthe end of the wire to be extracted.

We claim:
 1. Device for extracting screwthreaded wires forosteosynthesis, comprising at least two lever pieces (20-21, 120-121,220-221) hinged together and having at one longitudinal end thereof(20a-21a, 120a-121a, 220a-221a) seats or jaws (22-23, 122-123, 222-223)for grasping the end of a wire (19) which is required to be extracted,and manually operable clamp means acting on the other end (20b-21b,120b-121b, 220b-221b) of said lever pieces to promote opening or closingthereof to thereby generate at least one gripping couple on the end ofthe wire, and characterized in that said clamp means are provided withmeans (24-25, 128-129, 224-230) for preventing relaxation of the grip onthe end of the wire to be extracted, and said seats are provided withmeans (21-23, 122-123, 222-223) for gripping the end of the wire, saidrelaxation-preventing means (24-25, 128-129, 224-230) including at leasta threaded pin (24a, 124, 224) mounted at one end of one of the leverpieces for selectively locking the end of the other lever piece, saidgripping means (22-23, 122-123, 222-223) having semicylindrical cavitieswhose diameter is approximately equal to the diameter of the wire to beextracted and whose longitudinal axis is coaxial with the longitudinalaxis of the device, and having a first cylindrical end part (20a-21a,120a-121a, 220a-221a) whose diameter is slightly greater than thediameter of the wire to be extracted and a second, generallyfrustoconical part joining said first part and a generally cylindricalcentral part of the two lever pieces thereby to enable the wire to begripped beneath the surface of the skin.
 2. Device according to claim 1,in which the clamp means are of screw type.
 3. Device according to claim2, in which said means for preventing relaxation of the grip on the endof the wire to be extracted comprise at least one screwthreaded pin (24,124, 224) fitted with a knob and screwed into a tapped piece (25, 125,225) carried by the end of one of said lever pieces.
 4. Device accordingto claim 3, in which the axis of movement of said screw-type clamp meansis generally parallel with one of said lever pieces (20-21).
 5. Deviceaccording to claim 3, in which the axis of movement of said screw-typeclamp means is generally perpendicular to the longitudinal axis of thesaid device.
 6. Device according to claim 4, in which said hingingtogether of said two lever pieces is by a pivot, the end (24b) of thescrewthreaded pin (24) nearest the pivot being of a generallyfrustoconical shape to interact with an inclined plane surface (26)formed at the end (20b) of the other lever piece in such a way as toforce it outwards when said pin is screwed in.
 7. Device according toclaim 6, in which the hand of the thread on said pin (24) and on thetapped piece (25) is opposite to that of the thread on the wires. 8.Device according to claim 7, in which said pin (24) is provided, at theend opposite to the end (24b) having the generally frustoconical shape,with a knob having a generally polygonal cavity (40) whose longitudinalaxis is coaxial with the axis of said pin, which cavity is suitable forthe insertion of a polygonal socket wrench.
 9. Device according to claim8, in which said tapped piece (25) consists of a collar with a groovedsurface (27) suitable for use as a knob to provide a purchase during theextraction, by unscrewing, of the wire.
 10. Device according to claim 5,in which said pin (124) comprises two threaded portions (128 and 129)having threads of mutually opposite hand such that rotating said pin inone sense causes said tapped pieces and the corresponding ends of saidlever pieces to move together and rotating said pin in the other sensecauses said tapped pieces and the corresponding ends of the lever piecesto move apart.
 11. Device according to claim 10, in which said tappedpieces (125) are formed in two cylindrical pieces (150) each inserted inone of two corresponding cylindrical cavities whose axes are generallyperpendicular to those of the tapped pieces (125) located near the ends(120b, 121b) of said lever pieces (120 and 121).
 12. Device according toclaim 5, in which the lever piece opposite that on which said threadedpin (224) is mounted has a second knob (231) mounted on a fixed pin(230) that is generally coaxial with said pin (224).